1. Field of the Invention
The present invention relates to an image file system, and in particular, to a method for storing and displaying image data suitable for displaying at a high speed a retrieved image in an image file system.
2. Description of the Related Art
Recently, a document image file system (electronic file) using a large-capacity optical disk has become noticeable as a new means for document management. An optical disk has a large data storage capacity to record a great amount of data including the image data and therefore can be used as a store means storing document image information such as an account sheet, a design drawing, a contract, and the like. When retrieving these document images, it is desirable in ordinary cases to use an index such as a predetermined document name, classification name, keyword, or the like. When the index becomes to be complicated, however, it takes time to effect a job storing the document images together with the complex indices; furthermore, such a complicated index often becomes difficult to remember when a document is to be retrieved. To overcome this difficulty, only a simple index such as a classification name is often added to the document image for the storage in practice. Moreover, a stored image having a complex index added thereto is commonly retrieved by specifying only a simple index. In this case, to retrieve an objective document image, the operator must sequentially display on a display screen a plurality of candidate data retrieved by specifying an index such as a classification name so as to visually confirm the display contents, thereby extracting the objective document.
As a method for selecting the document image above, there has been a method, for example, described in pages 6-7 of the "Operation manual for Hitachi Optical Disk File System" (manual number 60-10-001-20) in which a previous page key or a next page key is used. According to this method, a sheet of image data is displayed on the screen each time the key is pressed. This method may be improved, for example, such that when a page change key is pressed, an automatic page change is effected for the retrieval data so as to sequentially display the data on the display screen until the next key depression is recognized as a termination command.
As described above, in the case where the document images obtained by the index retrieval (primary retrieval) are sequentially displayed so as to visually extract an object document therefrom (secondary retrieval), it is desired to increase the speed of the page change in a range in which the operator can judge whether the display document is an objective document or not, thereby minimizing a period of time required for the secondary retrieval. In the conventional retrieval system, however, the processing is achieved in a form that the document data attained by the primary retrieval is read from the document image file in a page-by-page (i.e. record-by-record) fashion so as to sequentially display the record data and the read speed of each image data is restricted by the performance of the file device; consequently, the cycle of the update of display content cannot be less than the time required to read data for a document, which leads to a problem that a wait time takes place to obtain the next screen.